1. Technical Field of the Invention
The present invention relates to a weft detecting device used in a loom such as an air jet loom, and particularly to a weft detecting device which detects a weft passing through a weft guide groove provided in a reed by a transmitted light.
2. Description of the Related Arts
Usually, a reed of an air jet loom comprises a number of dents of reed held parallel between an upper frame and a lower frame with each dent of reed having a shape projecting forwardly of the loom and a recess provided at the summit of the projection. The reed has a weft guide groove (weft flying path) formed of a number of recesses of the dents of reed. A weft is thrown in the loom by means of an air jet from a main air nozzle provided on the weft throwing-in (weft inlet) side of the loom and auxiliary air nozzle provided at a side of an the weft guide groove. And whether the weft has been regularly inserted or not is detected by a weft detecting device provided on the side opposite to the weft inlet side of the loom.
Various kinds of weft detecting device have been proposed. However, no weft detecting device having a sufficient detecting ability and being reliable and inexpensive has been provided yet.
For example, in Japanese Published Unexamined Patent Application No. 163448/1984, a weft detecting device is disclosed in which a plurality of light emitting optical fibers and a plurality of light receiving optical fibers are respectively bundled, and these bundles of optical fibers are inserted between dents of reed so as to be put in a weft guide groove provided in a reed from behind at a position near the limit of the weft reaching position of the weft guide groove on the side opposite to the weft inlet side. This weft detecting device is a reflecting weft detecting device in which a weft is detected by using an effect that a light emitted from the light emitting optical fibers is reflected by the weft and is incident onto the light receiving optical fiber.
However, in this reflecting weft detecting device in which a weft is detected by reflection of light (disclosed in Published Unexamined Patent Application No. 163448/1984), light is only a little reflected by some kinds of wefts, for example, a black and a transparent wefts, and therefore, the weft detecting sensibility of this device is low and the device as a whole is not so reliable.
Further, a weft detecting device is disclosed in Japanese Published Unexamined Utility Model Application No. 138886/1981 in which weft detecting means (a light emitter and a light receiver) are attached to a pair of (a right and a left) projections of a weft detecting member adapted to be inserted between dents of reed, and a flexible printed wire plate is adhered to one side surface of the weft detecting member, so that the weft detecting means are electrically connected through the flexible printed wire plate to an outer control section.
However, in this device disclosed in Japanese Published Unexamined Utility Model Application No. 138886/1981, since the light emitting element and the light receiving element are provided directly in the detecting section, the device cannot be made thin and therefore cannot be inserted between dents of reed. Further, because the size and shape of the elements are limited by the size and shape of the reed, the ability of the elements is limited. Consequently, it is difficult to accurately detect every change of the light amount caused when a thin weft passes throughout the whole of the weft passing region. Further, the reed moves back and forth during the weft throwing-in operation thereby pushing the weft in a space between the arranged warps. In an air jet loom, such a movement of the reed is made at a high speed, such as more than 600 times/min. However, in the prior art, no weft detecting device has yet been developed which has sufficient mechanical strength to withstand such shocks.
In a weft detecting device disclosed in Japanese Published Unexamined Patent Application No. 10456/1985, two extremely thin total reflection optical prisms are inserted between dents of reed so that lights cross the weft path between the prisms, whereby a weft is detected. The weft detecting device disclosed in Published Unexamined Patent Application No. 104560/1985 is a device for detecting a weft by a transmitted light in which optical elements comprising two prisms are provided in the weft guide groove and a weft is detected based on a change of light amount caused by the presence and the absence of the weft. Therefore, this device has no disadvantages of a weft detecting device of the reflection type. However, since the two prisms are not positioned in one united body and the light amount transmitted between prisms is changed by the shaking of the prisms during the operation of the loom, thereby causing noise, and only a low percentage of the light amount of the prisms is effectively used, the weft detecting sensibility of this device is low. Further, since the prisms are expensive, the manufacturing cost of the device becomes high.
As abovementioned, in the prior art, no weft detecting device has been developed which has a sufficient detecting ability and reliability, and is easy to treat and inexpensive. The reasons are that the size and shape of the detecting section are limited by the size and shape of a reed, and the detecting section hardly withstands the shocks more than 600 times/min. as abovementioned, and further, it is hard to prevent the adverse influence of dust upon the device when the operating loom is full of fibrous dust.